* Add missing includes
We would normally have these included in another file already, or even
the precompiled headers, but having the files included here too makes
testing single parts easier.
* Modify the regex building of highlight phrases for non-regex phrases
For phrases like !test, the word boundary checking we did before was not
enough, so we now check for either a word boundary, a whitespace
character, or the line start/end.
* Add tests for ensuring I haven't fully broken the highlight system
* Add changelog entry
